Acid-terminated hydroxy ester compounds as lubricating oil additives

ABSTRACT

NONCORROSIVE AND LOW-SLUDGING EP ADDITIVES FOR LUBRICATING OILS TO IMPROVE THE LOAD-CARRYING ABILITY OF SYNTHETIC ESTER LUBRICANTS ARE PROVIDED. THE ADDITIVE COMPOSITIONS OF THIS INVENTION ARE ACID-TERMINATED HYDROXY ESTER COMPOUNDS OBTAINED BY THE PARTIAL ESTERIFICATION OF A POLYBASIC ACID WITH A GLYCIDYL ESTER. THE EXTREME PRESSURE PROPERTIES OF SYNTHETIC ESTER LUBRICATING OIL COMPOSITIONS ARE SIGNIFICANTLY INCREASED BY INCORPORATING A SMALL AMOUNT OF COMPOUNDS SUCH AS HALF-ESTERS DERIVED FROM THE REACTION OF DIMER ACID AND A GLYCIDYL ESTER OF A BRANCHED-CHAIN ACID.

United States Patent Oflice 3,813,339 ACID-TERMINATED HYDROXY ESTER COM POUNDS AS LUBRICATING OIL ADDITIVES Raymond H. Boehringer, Cincinnati, Ohio, Ronald M.

Wilson, Edgewood, Ky., and Mark A. Margeson, Cincinnati, Ohio, assignors to Emery Industries, Inc., Cincinnati, Ohio No Drawing. Filed Aug. 2, 1972, Ser. No. 277,272 lug. Cl. C10m 1/26, N28

US. Cl. 252-56 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The use of aliphatic diesters and complex esters as synthetic lubricating oils has been widely accepted because of the outstanding viscosity properties of these compositions over a wide range of temperatuses. In certain applications, however, where severe operating conditions are encountered, the load-carrying ability of these synthetic lubicants is not sufiicient to provide adequate lubrication without the use of additional chemical agents to reduce the friction and the amount of Wear encountered. These additives, referred to as extreme pressure (EP) agents, are generally sulfur, chlorine, phosphorous or lead compounds which react with the surfaces of the metal to provide lubricant films capable of withstanding very high operating temperatures. While these additives effectively increase the loadcarrying ability of the lubricant system they also create corrosion, dirt and sludging problems particularly in systems where copper, magnesium, aluminum, silver and other metals are employed. 'In some cases, corrosion is so serious that it becomes more desirable to decrease the unit bearing load, improve the surface finish, increase the oil viscosity, use external pressurization or take similar measures rather than to incorporate an EP additive in the lubricant.

It would be desirable and highly advantageous if the load-carrying ability of synthetic ester lubricants could be increased without the addition of sulfur, chlorine, phosphorous and lead containing compounds and thus minimize or completely eliminate the corrosion and other problems normally encountered with these EP agents. It would be particularly useful if EP additives were available which could be easily prepared and which were readily compatible with synthetic ester lubricating oils.

SUMMARY OF THE INVENTION We have now discovered noncorrosive and low-sludging EP additives useful for synthetic ester lubricating oils to improve the load-carrying ability of the oils. The useful compositions of this invention are hydroxy ester compounds which contain at least one free carboxyl group and one radical derived from the reaction of a carboxyl group with a glycidyl ester. The glycidyl esters are derived from aliphatic acids containing from 5 to 22 carbon atoms. Especially useful glycidyl esters are derived from neoacids. Preferred hydroxy ester compositions are half-esters obtained from the reaction of about 0.45 to 0.55 equivalent of a neo-acid derived glycidyl ester with a dimer acid 3,813,339 Patented May 28, 1974 preferably containing by weight or more C dibasic acid. The useful EP additives are added to synthetic ester lubricants including diesters, polyesters and complex esters at levels ranging from 0.01% to about 5% by weight of the total lubricant.

DETAILED DESCRIPTION The hyroxy ester compounds of the present invention contain at least one free carboxyl group in the molecule and at least one group of the structural formula (I) ll I ll R-C O-OHzCHOHr-O C- in the molecular wherein R is a branched or straight chain alkyl group having from 4 to 21 carbon atoms. The radical I is obtained by the reaction of a carboxyl group with a glycidyl ester of an aliphatic acid containing from 5 to 22 carbon atoms.

Glycidyl esters employed to obtain the radical I are typically formed by the reaction of epichlorohydrin and alkali metal salt of the C aliphatic acid and have the general formula where R is the same as defined above for I. Preferred glycidyl esters are derived from branched-chain acids and have the general formula wherein R R and R are alkyl groups containing from 1 to 4 carbon atoms with the total number of carbon atoms in the three groups totaling from about from 4 to 10 carbon atoms. While the glycidyl esters derived from the neoacids are preferred for the present invention, glycidyl esters of pelargonic acid, heptanoic acid, valeric acid, isostearic acid, oleic acid and the like may also be conveniently employed.

Since the compositions of this invention necessarily contain a group of the formula I and also a free carboxyl group, the acids employed to prepare the hydroxy ester compounds must necessarily be dibasic, i.e., contain at least two carboxyl groups. While two carboxyl groups are essential to obtain the present compounds the acids may contain three, four or more carboxyl groups. As a practical matter, however, with increasing numbers of carboxyl groups present on the starting acid the complexity of the products is increased and the EP properties of the additives are not as great. When dibasic acids are used halfesters result. Irrespective of the number of carboxyl groups the acid should have a molecular'weight greater than about 480 and therefore must necessarily contain at least 30 carbon atoms. Acids meeting the above requirements are conveniently prepared by the polymerization of unsaturated monomer fatty acids containing from about 18 to 22 carbon atoms. These monomer acids contain one or more sites of unsaturation and include such acids as oleic acid, linoleic acid, eleostearic acid, ricinoleic acid, linolenic acid and the like. Processes for the formation of high molecular weight polymer acids are amply described in US. Pats. 2,482,761; 2,793,219 and 2,793,220. By varying the reaction conditions employed in the polymerization the ratio of dimer, trimer and higher acids may be varied.

Dimer acids obtained when two molecules of monomer acid are joined are particularly useful for the present invention. These acids are commercially available and sold under the name of Empol dimer and trimer acids (manufactored by Emery Industries, Inc.). The average number of carbon atoms in these products varies from about 36 to 54 carbon atoms. Preferred acids for the formation of the hydroxy ester additives of this invention contain at least 75 wt. percent C dibasic acid with the remainder of the acid composition being comprised of timer acid, i.e., C tribasic acids, and small amounts of tetramer or higher acids. Especially useful acid compositions contain 85% or more C dibasic acids The hydroxy ester compounds useful as EP agents for the present invention are obtained by the reaction of the above-described glycidyl ester and polybasic acids. This reaction is preferably carried out in the absence of a catalyst, however, a catalyst may be employed if desired to speed the rate of reaction. The reaction rates are generally suflicient so that catalysts are not necessary and also without the use of catalysts a purer reaction product is obtained and costly washing procedures to eliminate catalyst residue avoided. The reaction can be conducted over a wide temperature range but because it is desirable from an economic standpoint to have a rapid reaction rate, temperatures between about 150 C. and 250 C., and more preferably from 180 C. to 220 C. are employed. Reaction time is dependent on the temperature and particular reactants employed. Normally at a temperature of about 200 C. the reaction is run for about 1 to 2 hours. The ratio of reactants will be varied depending on the particular composition desired and the number of carboxyl groups on the acid to be reacted with the glycidyl ester. For example, with the preferred C dibasic acids about 0.3 to 0.7 equivalent glycidyl ester can be employed per equivalent dibasic acid with especially useful compositions being obtained with about 0.45 to 0.55 equivalent glycidyl ester per equivalent dibasic acid. Employing this latter range of reactants provides enough glycidyl functions to react with approximately half of the carboxyl groups thus giving half-esters. Where acids containing more than two carboxyl functions are used the equivalents ratio will be varied accordingly, but in no event will the glycidyl ester exceed an amount calculated to provide less than one free carboxyl group in the molecule. The compositions obtained may be a mixture of products, some of which contain more or less than the desired degree of substitution as long as the average composition meets the above-defined requirements, i.e., has at least one free carboxyl and at least one group of the type I.

The amount of hydroxy ester compound used may be widely varied but preferably these EP additives are present in the synthetic lubricant in amounts from about 0.01% to about 5% by weight of the total lubricant. Preferably the additives of this invention will be included in an amount ranging from about 0.1 to 1.5 wt. percent of the lubricant composition. At these levels the hydroxy ester compounds are effective EP agents improving the load-carrying ability of the lube and also significantly reduce metal corrosion and sludging in both petroleum and synthetic ester lubricants. The present additives may be employed with other materials commonly included in lubricant compositions such as oxidation inhibitors, detergents, dyes, antifoaming agents, viscosity improvers, additional corrosion inhibitors, -EP agents and the like. Compounds of the above types include p-aminodiphenylamine, phenyl-a-naphthylamine, phenothiazine, polymethylacrylates, silicon-containing polymers, polyisobutylenes, petroleum sulfonates, sorbitan monooleate, the barium salt of isononyl phenol sulfide, and the like. Normally these additional ingredients will constitute from about 0.01% to about by Weight of the total lubricant composition.

Lubricants for which the hydroxy ester compounds of this invention are useful additives are the synthetic ester lubricant oils including diesters, polyesters and complex esters. Diester lubricant oils are typically dicarboxylic acids fully esterified with monohydric alcohols and have the general formula wherein n is an integer ranging from about 6 to about 15 and R is a branched or straight chain hydrocarbon radical containing from about 1 to about 16 carbon atoms. Preferred diesters of the above type are derived from adipic acid, azelaic acid, and sebacic acid with a C or C branched-chain alcohol. Useful diester synthetic lubes include: di-Z-ethylhexyl sebacate, di 2 ethylhexyl isosebacate, di-n-nonyl adipate, di-n-heptyl isosebacate and the like. Also useful are diesters prepared from the Oxo alcohols which are mixtures of branched-chain aliphatic primary alcohols obtained by the reaction of olefin oligomers with carbon monoxide and hydrogen in the presence of a suitable catalyst followed by hydrogenation. Illustrative of such diesters are Ill-C Oxo adipate, di-C 0x0 adipate, di-C OX0 azelate, (ll-C7 Oxo adipate, di-C Oxo pimelate and the like. Diesters derived from the reaction of glycols fully esterified with monocarboxylic acids are also useful synthetic base lubricants for use with the EP additives of this invention.

Polyesters obtained from the reaction of polyhydric alcohols with monocarboxylic acids may also be employed as the synthetic oil. These include products derived from trimethylopropane and pentaerythritol With acids such as caproic acid, caprylic acid and pelargonic acid to give triesters and tetraesters, respectively. The polymeric forms of pentaerythritol may also be employed to obtain synthetic polyester lube oils. Complex esters used as synthetic base oils are those typically obtained from the esterification of a dicarboxylic acid with a glycol and a monofunctional alcohol or monocarboxylic acid. In general, a wide variety of ester base synthetic oils may be used and will have improved load-carrying properties when a small amount of the EP agents of the present invention are incorporated therein. The synthetic ester oils and methods for their preparation are known to the art and described in numerous patents and publications.

The following examples illustrate the invention more fully, however, they are not intended as a limitation of the scope thereof. In these examples all weights and percentages are on a weight basis unless otherwise indicated.

Example I An acid-terminated hydroxy ester compound having essentially the formula was prepared by reacting 1 mol (586 grams) of a C dibasic acid having a molecular weight of approximately 565 (Empol 1010 Dimer Acid) with a mol (245 grams) of a glycidyl ester of a neo-acid having an average molecular weight of about 245 (Cardura E). The reaction was conducted at 220 C. for one-half hour under a nitrogen blanket. The final product had an acid value of 39, hydroxyl value of 68, a 520 F. fiashpoint and firepoint of 630 F.

Example II The half-ester prepared in Example I was evaluated in a synthetic ester base lubricant. The base lubricant employed was a blend of about 93 parts of a complex ester derived from monopentaerythritol and esterified with a mixture of acids comprising about 50% isovaleric acid, 25% pelargonic acid and 25% of a mixture of C to C monobasic acids (Emfac 1210 Low Molecular Weight Acid) and about 7 parts of a polyester comprised of the reaction product of 1 mol azelaic acid, 2 mols monopentaerythritol and 4 mols of a mixture of C to C monobasic acids (Emfac 1210). The EP agents of Example I were incorporated in the base lubricant at a 0.5% and 1.0% level and the load-carrying ability of the lubricating oils measured with a Ryder Gear Machine in accordance with Federal Test Method Standard No. 791a, Method 6508. Results obtained are reported in Table I. The data clearly demonstrates that by incorporating a small amount of the hydroxy ester compounds in synthetic ester lubes the load-carrying ability of the lubricant is significantly increased. It is further observed that the so-compounded lubricating oils have excellent oxidative stability, are resistant to sludge buildup and have extremely low corrowherein R is a branched or straight chain radical containing from 4 to 21 carbon atoms, said hydroxy ester compound containing on an average one free carboxyl group.

2. The lubricant composition of claim 1 wherein the glycidyl ester is derived from neo-acids and has the siveness to copper, magnesium, iron, aluminum and lead. 5 formula Similar results are obtained with other synthetic ester R1 0 lubes containing the hydroxy ester additive. I

The unexpectedness of the finding that hydroxy ester O CH-CH CH compounds function as acceptable EP additives for syn- 2 thetic ester lubricants is demonstrated when structurally h i R R d R are lk l groups t i i f m similar additives were p y with no significant 1 to 4 carbon atoms with the total number of carbon provement in the EP properties. For example aC dibasic atoms in the three groups totaling from about 4 to 10 acid was fully esterified with a 50-50 mixture of methyl carbon atoms.

TABLE I Test oil rating Pounds Relative per inch Reference rating, SldeA SideB (average) average percent Base lubricant 2, 540 2, 289 2, 415 2, 920 82. 7 Base lubricant with- 0.5% hydroxy ester udditive-. 2, 648 3,102 2,875 2, 940 97.8 1.0% hydroxy ester additlve 2, 805 2, 872 2, 839 2, 920 97. 2

alcohol and Z-ethylhexyl alcohol and a half-ester of the 3. The lubricant composition of claim 2 wherein the C disbasic acid prepared with methyl alcohol and evaludibasic acid is a dimer acid and contains 85% or more ated in synthetic ester base oils. No significant improve- C dibasic acid and is reacted with about 0.45 to 0.55 ment in the load-carrying ability was observed in either equivalent glycidyl ester per equivalent dibasic acid. case, in fact, with the complete ester a substantial decrease 4. The lubricant composition of claim 3 wherein the in lubricity was noted when subjected to the Ryder Gear hydroxy ester compound is essentially a half-ester of the Test. formula We claim: 0 0H 0 1. A noncorrosive, low-sludging synthetic ester lubricat- I ing composition having improved EP properties compris- Claim-J; (Pomflcflro & C"HCOOH ing major amounts of a synthetic ester lubricant selected References Cited from the group consisting of diesters, polyesters and complex esters and from about 0.01% to about 5% by weight, UNITED STATES PATENTS based on the total lubricant composition, of a hydroxy 3,017,359 1/1962 Gottshall et al. 252-57 X ester compound obtained from the reaction of a dibasic 3,223,635 12/1965 Dwy r t l- 25256 X acid obtained by polymerizing an unsaturated fatty acid 3, 10/1969 Boehl'inger et a1 57 and containing from about 36 to 54 carbon atoms and con- 3,485,754 12/ 1969 Boylan et al. 252-57 X taining at least by weight C dibasic acid with a glycidyl ester of the formula WARREN H. CANNON, Primary Examiner US. Cl. X.R. 

